Exercise induced paradoxical vocal fold motion (EI-PVFM) is a condition which symptoms include breathing difficulty and stridor during exercise, particular in adolescent athletes. Because its symptoms mimic exercise induced asthma, it is often treated with asthmatic medications. Poor response of EI-PVFM to these medications results in increased dosage and complications from long-term use. The optimal treatment for EI-PVFM is behavioral therapy provided by speech-language pathologist. Accurate diagnosis leads to effective treatment outcome that will help these young athletes to return to practice and avoid misuse of medical resources. Thus, definitive diagnostic tools are needed to identify patients with vocal cord dysfunction and evaluate their treatment outcome. The current "gold standard" for diagnosing EI-PVFM is the expensive and invasive laryngoscopy. Other alternatives have their respective disadvantages. For instance, the spirometry has low sensitivity (23%) and dependent on the child's effort to obtain accurate measurement;the methacholine challenge test has low specificity (30%);the body plethysmography is cumbersome and expensive. The investigators have previously developed a portable airflow perturbation device (APD) that can measure inspiratory and expiratory respiratory resistance under natural breathing condition that requests minimal cooperation from the examinee that includes no more than normal breathing for less than a minute. As previously reported and recently discovered in our preliminary study, the inspiratory resistance increased when the patient with EI-PVFM was symptomatic, whereas it decreased at rest or after effective breathing training. Major advantages of the APD include non-invasiveness, ease of use (requiring natural breathing for less than 1 minute), child-friendly (even for 2-year-old children), portability (applications at various sites), and relatively less effect by airflow leak at the mouthpiece. Phase I funding will enable us to investigate the feasibility of using the APD as a diagnostic tool for EI-PVFM and test its sensitivity and specificity comparing to laryngoscopic exams in wider range applicable to EI-PVFM. In Phase II we plan to improve the flow sensor's accuracy and sensitivity, and add configurations to be used during exercise with additional measurements including flow-volume display, and test the device/method using large pediatric population including minorities and ethnic groups. To bring APD into commercial production (our long term objective) for this new application, further development and refinements are necessary. After that, clinical data must be obtained, and regulatory approval must be sought. The market for this application of the APD is very wide, including clinics, physician's offices, sport training sites, schools, and for a large number of pediatric population involved in a variety of sport activities. Because of its portable size, low cost, and ease of operation, the APD is an ideal device for monitoring at sport training sites. In Phase II we plan to test the device on at least 400 individuals at different clinics. PUBLIC HEALTH RELEVANCE: Exercise-Induced respiratory disorder is very common among your athletes (mostly girls) and is usually undetected or misdiagnosed/mistreated. We are proposing a simple diagnostic/management device that is non-invasive, effortless, simple, and at low cost compared to the invasive and expensive laryngoscope.